There are only a relatively few pediculicides which are commercially available today. The most popular pediculicidal toxicants are Lindane (gamma benzene hexachloride), Malathion (S-1,2-dicarbethoxyethyl)-0,0-dimethyl phosphorodithioate), synergized pyrethrins and Cuprex (a combination of tetrahydronaphthalene, copper oleate and acetone, the acetone not asserted to be active).
Because of increased concern about the overall safety of some of the known ectoparasitic toxicants, the search for new, safe and effective pediculicides has intensified recently. It has now been discovered that the combination of an aliphatic alcohol and an aliphatic ester is synergistic as a pediculicide.
The results achieved in the instant invention are particularly surprising in view of the prior art. For example, one of the preferred ingredients, isopropanol has been used in Great Britain as a solvent for the Lindane and Malathion toxicants for some time. Additionally, investigations of the effect of various solvent system combinations for increasing the penetration of primary toxicants have been made. Wigglesworth, in "Permeability of Insect Cuticle," Nature, 147, 116 (January 1941), and "Some Notes on the Integument of Insects in Relation to the Entry of Contact Insecticides," Bull. Ent. Res., 33 205, (1942) describes the effect of oils and mixtures of oil and alcohol on insects including the louse. Hurst, in "Insect Cuticle as an Asymmetrical Membrane," Nature 147, 338 (March 1941), "Permeability of Insect Cuticle," Nature, 145, 462 (March 1940) and "Principals of Insecticidal Action as a Guide to Drug Reactivity--Phase Distribution Relationships," Trans. Faraday Soc. 39, 390 (1943), describes a mixture of kerosene and ethyl alcohol. However, Wigglesworth, Hurst, and others failed to perceive that such solvent systems, appropriately modified, could be used as pediculicides without the addition of a "primary toxicant." For example, McKim described the combination of a toxicant with a mixture of lower aliphatic alcohol and a hydrocarbon oil in U.S. Pat. No. 2,396,054 (1946). Moreover, both Wigglesworth and Hurst believed desiccation and imbibition were the means by which the polar/apolar combinations caused distress to insects. The findings that the instant pediculicides exhibit high activity in the presence of high percentages of water is therefore particularly surprising.
It is the object of this invention to provide new, safe and effective pediculicides and also to provide a safe and effective treatment for the control of ectoparasites such as lice. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.